Method for detecting objects in a warehouse and/or for spatial orientation in a warehouse

ABSTRACT

A method for detecting objects in a warehouse and/or for spatial orientation in a warehouse includes:
         acquiring image data with a 3-D camera which is fastened to an industrial truck so that a viewing direction of the 3-D camera has a defined horizontal angle, wherein the 3-D camera has an image sensor with sensor elements arranged matrix-like and the image data comprises a plurality of pixels, wherein distance information is assigned to each pixel,   calculating angle information for a plurality of image elements, which each specify an angle between a surface represented by the image element and a vertical reference plane,   determining a predominant direction based on the frequency of the calculated angle information,   calculating the positions of the of the acquired pixels along the predominant direction,   detecting at least one main plane of the warehouse based on a frequency distribution of the calculated positions.

BACKGROUND OF THE INVENTION

The invention relates to a method for detecting objects in a warehouseand/or for spatial orientation in a warehouse, in which image data isacquired and evaluated. For this purpose it is known in the field ofwarehouse logistics to equip industrial trucks with laser scanners.These, in particular in combination with reflective markers positionedin the warehouse, can deliver information about the position of theindustrial truck in the warehouse, and in this manner supplement orcompletely replace other navigation systems. The use of laser scannersis known also for supporting storage and retrieval procedures.

It is known from the document EP 2 468 678 A2 to arrange atime-of-flight camera system on an industrial truck, and in this mannerto acquire a three-dimensional image of the surroundings of theindustrial truck. This is used in particular for supporting an operatorin that storage and retrieval procedures are automated to some extent.

Based on this background, the object of the invention is to provide amethod for detecting objects in the warehouse and/or for spatialorientation in a warehouse, with which the acquisition and evaluation ofthree-dimensional image data is better adapted to the specific useconditions of an industrial truck so that it can be implemented easilyand reliably, and an industrial truck suited for this purpose.

SUMMARY OF THE INVENTION

This object is solved by the method with the features of claim 1.Advantageous designs are specified with the subsequent sub-claims.

The method serves for detecting objects in a warehouse and/or forspatial orientation in a warehouse and has the following steps:

-   -   acquiring image data with a 3-D camera which is fastened to an        industrial truck so that a viewing direction of the 3-D camera        has a defined angle to the horizontal, wherein the 3-D camera        has an image sensor with sensor elements arranged matrix-like        and the image data comprises a plurality of pixels, wherein        distance information is assigned to each pixel,    -   calculating angle information for a plurality of image elements,        which specify an angle between a surface represented by the        image element and a vertical reference plane,    -   determining a predominant direction based on the frequency of        the calculated angle information,    -   calculating the positions of the acquired pixels along the        predominant direction,    -   detecting at least one main plane of the warehouse based on a        frequency of the calculated positions.

The image data acquired with the 3-D camera is a spatial image of thesurrounding area because distance information is assigned to each pixel.Such image data is also called a cluster of points. The cluster ofpoints contains a plurality of points whose arrangement in space isdescribed by the specification of the coordinates in a three-dimensionalcoordinate system. A Cartesian coordinate system, for example, whoseaxes directions have a fixed orientation relative to the viewingdirection of 3-D camera can be used for this purpose. For example, thex-axis can point in the viewing direction of the 3-D camera toward theright, the y-axis can point perpendicularly downward, and the z-axis canpoint in the viewing direction of the 3-D camera. The image sensor hassensor elements arranged matrix-like, for example in a rectangularraster having 640×480 sensor elements. Each sensor element cancorrespond to a pixel. In order to assign distance information to eachpixel, different techniques are used depending on the type of the 3-Dcamera being used. For example, the 3-D camera supplies image datahaving 640×480 pixels which are identified by their x, y, and zcoordinates.

With the invention, angle information is calculated for a plurality ofimage elements. Each image element can be an individual pixel, or aplurality of mathematically combined pixels. Each image elementrepresents a surface, that is, a surface of an object in the image fieldof the 3-D camera, more or less facing the 3-D camera. The angleinformation describes an angle between this surface and a verticalreference plane. The vertical reference plane can be a vertical plane inthe viewing direction of the 3-D camera for example. In the above namedexample of a coordinate system this would be the y-z plane. However,another vertical plane can also be used as the reference plane, inparticular a vertical plane arranged fixed relative to the arrangementof the 3-D camera.

In order to calculate the necessary angle information, initially anormal vector on the surface represented by the image element can becalculated. Then, the angle between this normal vector and the referenceplane can be calculated. This corresponds to a projection of the normalvector onto a horizontal plane in which the angle to the reference planecan be shown.

A predominant direction is determined based on the frequency of thecalculated angle information. A histogram of calculated angleinformation can be created for this purpose, wherein all calculatedangles which are located in specific angle intervals, are summed Themaximum of this histogram specifies in which of the angle intervalsthere is the largest number of the tested image elements relative to thereference plane. This most frequently occurring alignment of the imageelements relative to the reference plane represents a predominantdirection.

After determining the predominant direction, the positions of theacquired pixels are calculated along the predominant direction. Thesepositions correspond to the distances of the individual pixels from animaginary plane that is perpendicular to the predominant direction.Mathematically this can be accomplished, for example, by a coordinatetransformation into a new coordinate system, wherein one of the axes ofthe new coordinate system is aligned in the predominant direction. Then,the coordinate of a pixel for this axis direction corresponds to theposition to be calculated.

Finally, a main plane of the warehouse is detected based on a frequencydistribution of the calculated positions. For this purpose a histogramcan also be created, this time for the calculated positions, which inturn can be “sorted into” position intervals of predetermined size. Amaximum of this frequency distribution indicates that at the associatedposition, thus, in a plane perpendicular to the predominant direction, aparticularly large number of pixels were detected at this specificposition along the predominant direction. Therefore, this planerepresents a main plane of the warehouse. The maximum of the frequencydistribution of the calculated positions can be an absolute maximum or alocal maximal. If the frequency distribution has several maximums,several main planes of the warehouse can also be detected in thedescribed manner.

The detection of main planes provides a spatial orientation in thewarehouse because the detected main planes represent, in particular,distinctive structures in the warehouse. However, if the method is usedfor detecting objects in the warehouse, on the one hand the detection ofthe main plane can be connected with specific objects and are as suchdetected. On the other hand a further evaluation of the image datautilizing the detected main planes can occur, whereby—as will bedescribed below—further objects can be detected particularly easily inaddition to the main planes.

With the invention, the typical conditions of warehouses administeredwith industrial trucks are exploited. The inventors have recognized thatthe essential structures of such warehouses, for example walls, shelves,individual shelf support, pallets or transport containers stored on theshelves, wall and cover surfaces, etc. are generally arranged at rightangles to each other. Here, the horizontal and the vertical directionsplay a special role that are typically strictly adhered to by the floorsurfaces of individual warehouse spaces, and respectively the mostdifferent vertical supports and many other lateral surfaces. Due tothis, typical warehouses differ substantially from other environments,for example, the surroundings of a motor vehicle traveling on a highway.

The invention exploits these particular conditions of typical warehousesin order to specifically simplify the evaluation of the image data whichis very time consuming and computationally intensive. Thus, the factthat the viewing direction of the 3-D camera has a defined angle to thehorizontal is utilized with the calculation of the angle information sothat angle information with respect to the vertical reference plane canbe calculated directly. The subsequent evaluation steps are basedsubstantially on frequency distributions, which is particularly easywith a computer-supported evaluation of the image data. As a result, therelevant main planes of the warehouse can be detected with lowcomputational expenditure, that is with relatively inexpensive computersand/or particularly quickly, and however still reliably.

In one design, the image elements for which the angle information iscalculated, are calculated in each case by averaging all pixelscontained in a specified volume element. In principle, angle informationcan be calculated for each acquired pixel. In order to be able tointerpret the individual pixels as a surface with a defined direction,the evaluation must consider adjacent pixels. The calculation of theangle information is therefore relatively time-consuming If a pluralityof the acquired pixels are combined using averaging into one imageelement that then represents a larger surface of the acquired scene,correspondingly less angle information must be calculated. The averagingcan occur over all pixels contained in a specified volume element, thatis, the space populated by the cluster of points is divided into aplurality of uniform cubic volume elements. For example the volumeelements, also called a voxel, can have edge lengths in the range of 5cm to 40 cm, preferably approximately 20 cm. Tests have shown that evenwith use of such a relatively coarse raster, the main planes of atypical warehouse environment are reliably detected. At the same time,the computation time for the evaluation of the image data issignificantly reduced because the averaging over the pixels of thevolume element is performed substantially faster than the calculation ofa corresponding larger amount of angle information.

In one design, one of the main planes is a wall plane, which is detectedat a first position and perpendicular to the predominant direction, ifthe frequency distribution at the first position has a first maximum andthe number of the pixels with positions further remote from theindustrial truck is less than a preset first limit value. Wall surfacesof the warehouse located in the image field of the 3-D camera generallylead to a distinct maximum in the frequency distribution of thepositions. Characteristic for wall surfaces here is that no furtherpixels are located behind, thus at greater distances from the industrialtruck. If these conditions are present, a wall plane is detected. Withthe detection of the wall plane, the preset first limit value excludesindividual pixels acquired behind the wall plane probably due tomeasurement errors (noise).

In one design, one of the main planes is a shelf front plane, which isdetected at a second position and perpendicular to the predominantdirection if the frequency distribution at the second position has asecond maximum and the second position is arranged closer to the 3-Dcamera than the first position by 0.9 m to 1.7 m. A shelf front plane isthe closest front surface of a shelf facing the 3-D camera. With typicalwarehouses, the shelf front plane is frequently located at a distance ofapproximately 1.2 m in front of a wall. If the wall remains visiblethrough the shelf at least to some extent, a histogram of the positionsprovides two maximums: a first maximum at a greater distance from the3-D camera, which characterizes the wall plane, and a second maximum ata second position in the range of 0.9 m to 1.7 m in front of the wallplane. If these conditions are present, a shelf front plane is detectedat the second position.

In one design, one of the main planes is a shelf front plane, which isdetected at a third position and perpendicular to the predominantdirection if the frequency distribution has only a single distinctmaximum that is arranged at the third position, and the number of pixelswith positions further remote from the 3-D camera is greater than apredefined second limit value. This constellation results in a typicalwarehouse when no wall is visible behind the shelf. In this case, thereis a single distinct maximum in the histogram of the positions at thelocation of the shelf front plane. The pixels acquired behind the shelffront plane can be caused by stored items or rear shelf supports. Theirnumber exceeds the predefined second limit value and aids detecting asingle distinct maximum as a shelf front plane and not as a wallsurface.

In one design, the method has the following further steps:

-   -   projecting the pixels, which lie in a surrounding area of a        detected main plane onto this main plane, and    -   detecting objects of the warehouse using comparison of the        projected, two-dimensional data with predefined templates.

In other words, the detected main plane is used for detecting furtherobjects in the warehouse. For this purpose, pixels which are located ina surrounding area of the main plane are initially projected onto themain plane. The surrounding area can be characterized, for example, by apredefined distance range from the detected main plane. For example, allacquired pixels which are located at a distance of less than 25 cm infront of the detected main plane and less than 1.2 m behind the detectedmain plane, are projected onto the main plane. In this example, if thedetected main plane is a shelf front plane, even with consideration oftolerances with acquiring the pixels, all pixels which belong to objectswithin the shelves are included in the further evaluation. After theprojection of the thusly preselected pixels onto the main plane, thereis a further evaluation based on the projected, two-dimensional data.This is therefore computationally less intensive. With the design,pattern detection methods in which the projected, two-dimensional dataare compared with predefined templates are used. These methods are alsoknown as “template matching”. One advantage of using a 3-D camera as abasis for this template matching method is that the data to be evaluatedhas the proper scaling, which simplifies the template matching. With thetemplate matching, initially using the named comparison, degrees ofsimilarity are determined between the predefined template and thespecific region of the projected, two-dimensional data. These correspondto probabilities that the acquired data are traced back to an objectcorresponding to the predefined template. For specific structuresextending frequently beyond the height or width of the image, the thuslydetermined degrees of similarity can be summed by rows or by columns.For example, for detecting horizontal shelf supports, the determineddegrees of similarity are summed by rows. The rows with the overallhighest degree of similarity represent a horizontal shelf-support withhigh probability. This is also true for vertical shelf supports withwhich the degrees of similarity that are found are added on a columnbasis.

A subsequent plausibility assessment can be added to the statedevaluation steps. If pallets are detected with the template matchingthat are, for example, not located within 20 cm above a horizontal shelfsupport or above the floor, these cannot be pallets. In this case nopalette is detected at the cited location. The same is true for a palletwhose position is intersected by a vertical shelf support. In this case,either the first detected object is not a pallet or the second detectedobject is not a vertical shelf support.

The object specified above is also solved by the method with thefeatures of claim 7. Advantageous designs are specified in thesubsequent sub-claims.

The method serves for detecting objects in a warehouse and/or forspatial orientation in a warehouse and has the following steps:

-   -   acquiring image data with a 3-D camera which is fastened to an        industrial truck so that a viewing direction of the 3-D camera        has a defined angle to the horizontal, wherein the 3-D camera        has an image sensor with sensor elements arranged matrix-like,        and the image data comprises a plurality of pixels, wherein a        color value and distance information is assigned to each pixel,    -   segmenting the image data into contiguous segments based on the        color value,    -   calculating segment attributes for each segment,    -   classifying the segments based on the segment attributes,    -   detecting a warehouse object based on the classification.

With respect to acquiring the image data, reference is made to thepreceding explanation. A difference consists in that now in addition todistance information associated with each pixel, a color value is alsoacquired for each pixel.

After acquiring the image data, these are segmented into contiguoussegments based on the color value. The individual segments comprisepixels which are in a logical relationship. For the segmenting, theknown Felzenszwalb-Huttenlocher algorithm can be used for example.

Subsequently, segment attributes are calculated for each segment thatthen form the basis for a classification of the segment. The detectionof a warehouse object occurs then based on the classification.

This method also allows individual warehouse objects to be detected, orto be spatially oriented in the warehouse based on the detected objects.The segmenting of the image data at the very beginning of the evaluationsimplifies the subsequent evaluation steps, which makes the methodparticularly practical for use in conjunction with an industrial truck.

In one design, one or more of the following properties are used assegment attributes: dimensions, average color value, number of pixels,relative depth information. For calculating the dimensions of thesegments, initially the alignment of the respective segment must bedetermined For this purpose, the largest surface of the segment can bedefined as the front side, for example. This definition can occur basedon an evaluation of the most frequent normal directions of the pixelsbelonging to this segment, or respectively of the surfaces representedby these, as described in detail in conjunction with the first methodaccording to the invention. In order to keep the computational expenselow, processing work can be performed again using image elements whichrepresent a plurality of the acquired pixels, for example again byaveraging. The division of the overall image volume used for allocatingthe acquired pixels can in turn occur using equally sized cubes, forexample having a uniform edge length of approximately 5 cm. Thedimensions can be acquired in three dimensions, wherein each segment canbe approximated as a cuboid. The relative depth information can becalculated from the difference of an object farthest remote from the 3-Dcamera (for example a wall surface) to the object in the viewingdirection(i.e. at the same angle about a vertical axis) and the distanceof the object from the 3-D camera. This relative depth informationallows a simple evaluation of the in front/behind relationship betweendifferent segments.

Also, as with the dimensions, the average color value of individualsegments can also provide important information about the objectrepresented by the segment in question. For example, pallets generallyhave a gray-brown color, whereas shelf supports are also painted in atypical color. Thus, the segment attribute “average color value” alsoprovides important information for the proper classification of thesegment. The number of pixels of a segment also has significance for theproper classification. In particular, in conjunction with a simultaneousdetermination of the segment attribute “dimensions”, the number ofpixels can provide information about the closedness of the surface.

In one design, a “support vector machine” is used for theclassification. A support vector machine is a computer program that isused for classifying objects based on a machine training procedure. Eachobject to be classified is represented by a vector in a vector space.With the invention, the objects to be classified are the segments whichare each described by a vector. The vector contains all the segmentattributes assigned to the segment in question. Training objects thatbelong to the predefined classes are used for “training” the supportvector machine. For example, the known objects in a data set acquiredwith the 3-D camera can be manually assigned to the predefined classesfor this purpose. Based on such training data sets, the support vectormachines learn proper classification of the segments. The result is areliable classification with relatively low computational expense and anongoing optimization of the classes used, without having to performsubstantial theoretical considerations for the individual segmentattributes of the predefined classes. As a result, the method isparticularly simple and automatically adapts to the respectivecircumstances. Properties of typical warehouses that many warehouseshave in common—for instance the presence of vertical shelf supports—butalso individual warehouse circumstances, for example the lightingsituation count among these circumstances.

In one design, one or more of the following classes are considered withthe classification of the segments: vertical supports, horizontal shelfsupport, signs, transport boxes, walls, pallets. In particular, all ofthese classes can be considered, and thus the entirety of the objectspresent in a typical warehouse are completely classified to a largeextent.

In one design, segments lying above one another which were classified asa vertical shelf support, and/or segments lying next to each other,which were classified as a horizontal shelf-support, are combinedrespectively into a segment group. Segments lying above one anothermeans segments which are arranged at the same lateral position in thewarehouse but at different heights. Correspondingly, segments lying nextto each other means segments which are located at the same height buthave a lateral distance from each other. The segment groups formed inthis manner represent the entirety of a horizontal, or a vertical, shelfsupport, even when this was only detected piecewise. Likewise it is alsopossible to expand the thusly formed segment groups, namely by segmentsnot classified as vertical or horizontal shelf support that are locatedbetween two segments classified as such. In this case, the segmentgroups then comprise in each case the entirety of a horizontal or avertical shelf support.

In one design, a segment is detected as a pallet if the followingcriteria are satisfied:

-   -   the segment was classified with a minimum probability as a        pallet and/or    -   a center point of the segment is located within a predefined        height range above a horizontal shelf-support and within a        predefined distance range behind the front and/or    -   a comparison of the front side of the segment with a predefined        template of a pallet yields a minimum degree of similarity.

In particular, a segment can be detected as a pallet only when all threecriteria are satisfied. The criteria are a type of plausibilityassessment for the detection of a pallet. Not only the classification ofthe respective segment is considered, but also the arrangement of thesegment relative to a horizontal shelf support and, if applicable,additionally the agreement of a front side of the segment with apredefined template. For the methods used here for the templatematching, reference is made to the explanations above, which areapplicable correspondigly. On the whole, by satisfying the criteria, aparticularly high probability is attained that a segment detected as apallet actually represents a pallet.

In one design, a vacant warehouse space is detected if there are nopixels, or respectively segments, present in a defined spatial regionabove an object that was detected or classified as a horizontal shelfsupport. In this manner, based on each of the two methods according tothe invention, warehouse spaces can be made detectable.

In one design the dimensions of a load are determined by evaluation ofthe pixels, or respectively segments, acquired above an object detectedas a pallet. In particular, all acquired pixels, or respectivelysegments, that are arranged beneath a horizontal shelf support detectedabove the pallet can be considered. The dimensions of the load can inturn be approximated by a cuboid that encloses all pixels acquired abovethe pallet.

In one design, the industrial truck has a navigation system thatprovides position data for the position of the industrial truck in thewarehouse, and the position data are adapted under consideration of adetected main plane and/or a detected object. In principle, anorientation can be established in the space using only the methodaccording to the invention so that a conventional navigation system isnot necessary. In the named design however, the method is combined withsuch a navigation system. Then each of the methods according to theinvention can be used for refining the position data which was acquiredusing the conventional navigation system. The conventional navigationsystem can for example provide a location of the position of theindustrial truck using radio, or by means of one or more laser scanners,or by means of odometry. By considering the main planes and/or objects,the position data provided by such a system can be corrected and canpossibly be made substantially more precise.

In one design, the 3-D camera is a time-of-flight camera or a camerasystem that projects and maps a defined template on the image field, andfrom a shift of the template determines the distance information.Time-of-flight cameras are known for acquiring three-dimensional imagedata. They illuminate the image field with a modulated light intensity,in particular in the infrared range, and evaluate a phase shift of thelight signal reflected by the objects located in the image range. Thephase shift arises due to different travel times of the light on thepath from the light source arranged integrated in the 3-D camera, ornear the 3-D camera, to the reflecting items and back. The Kinect Systemfrom Microsoft is a known camera system that acquires distanceinformation based on a projected template. It combines a two-dimensionalVGA camera with a distance measuring system that is based on thetriangulation principle.

The object specified above is also solved by an industrial truck withthe features of claim 17. The industrial truck has an apparatus fordetecting objects in a warehouse and/or for spatial orientation in awarehouse, wherein the apparatus comprises the following:

-   -   a 3-D camera for acquiring image data, wherein the 3-D camera is        fastened to the industrial truck so that a viewing direction of        the 3-D camera has a defined angle to the horizontal, an image        sensor having sensor elements arranged matrix-like and the image        data comprises a plurality of pixels, to each of which distance        information is assigned,    -   an evaluation apparatus for evaluating the image data that is        designed for the purpose of calculating angle information, which        each specify an angle between a surface represented by the image        element and a vertical reference plane, for a plurality of image        elements, based on the frequencies of the calculated angle        information determining a predominant direction, calculating        positions of the acquired pixels along the predominant        direction, and detecting at least one main plane of the        warehouse based on a frequency distribution of the calculated        positions.

For explanation, reference is made to the explanation above for thecorresponding method. The industrial truck is equipped for performingthis method. It is understood that also all particulars of the inventiondescribed above in conjunction with the industrial truck according tothe invention can be used. For this purpose in particular the evaluationapparatus can be designed for performing the method steps of one or moreof the sub-claims 2 to 6 or 13 to 15. The 3-D camera can be designedcorresponding to the features of claim 16.

The object specified above is also solved by the industrial truck withthe features of claim 18. The industrial truck has an apparatus fordetecting objects in a warehouse and/or for spatial orientation in awarehouse, wherein the apparatus comprises the following:

-   -   a 3-D camera for acquiring image data, wherein the 3-D camera is        fastened to the industrial truck so that a viewing direction of        the 3-D camera has a defined angle to the horizontal, an image        sensor having sensor elements arranged matrix-like, and the        image data comprises a plurality of pixels, to each of which a        color value and distance information is assigned,    -   an evaluation apparatus for evaluating the image data that is        designed for the purpose of segmenting the image data into        contiguous segments based on the color value, calculating        segment attributes for each of the segments, classifying the        segments based on the segment attributes, and detecting a        warehouse object based on the classification.

For explanation, reference is made to the explanation above for thecorresponding method. The industrial truck is equipped for performingthis method. It is understood that also all particulars of the inventiondescribed above in conjunction with the industrial truck according tothe invention can be used. For this purpose the evaluation apparatus canin particular be designed for performing the method steps of one or moreof the sub-claims 8 to 15. The 3-D camera can be designed correspondingto the features of claim 16.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail below based on twoexemplary embodiments shown in several figures. The figures show:

FIG. 1 a schematic representation of a warehouse from above,

FIG. 2 an illustration of a cluster of points,

FIG. 3 a histogram for angle information of image elements,

FIG. 4 a histogram of the positions of the acquired pixels along apredominant direction,

FIG. 5 a further histogram of the positions of the acquired pixels alonga predominant direction for another image data set,

FIG. 6 a two-dimensional representation of the pixels acquired in asurrounding area of a shelf front plane,

FIG. 7 a predefined template that represents a horizontal shelf support,

FIG. 8 a predefined template that represents a vertical shelf support,

FIG. 9 a predefined template that represents a pallet,

FIG. 10 a diagram for the results of a comparison of the data from FIG.6 with the predefined template from FIG. 7,

FIG. 11 a diagram for the results of a comparison of the data from FIG.6 with the predefined template from FIG. 8,

FIG. 12 a diagram for the results of a comparison of the data from FIG.6 with the predefined template from FIG. 9,

FIG. 13 a representation of image data divided into a plurality ofsegments,

FIG. 14 a schematic representation for determining the dimensions of asegment,

FIG. 15 a schematic representation for the definition of a relativedepth information,

FIG. 16 the image data represented in FIG. 13 after a classification.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic view of a typical high-bay warehouse fromabove. The warehouse comprises three wall surfaces 10 aligned verticallyand at right angles to each other. A shelf 12 is located in each case infront of two of the wall surfaces 10 that are across from each other.The front sides of the shelves 12, removed from the wall surfaces 10,are each located in a shelf front plane 14.

The warehouse is managed by an industrial truck 16 which has a 3-Dcamera 18. The 3-D camera 18 is fastened to the industrial truck 16 sothat the viewing direction thereof has a defined angle to thehorizontal. A coordinate system indicated in FIG. 1 is alignedcorresponding to the viewing direction of the 3-D camera 18, the z-axisof which is in the viewing direction of the 3-D camera 18. The x-axis ofthis coordinate system points toward the right in the viewing directionof 3-D camera, and the y-axis, not shown, points downward. Theindustrial truck 16 has a main travel direction in the direction towardthe indicated load support means 20 that corresponds to the z-axis inthe viewing direction of the 3-D camera 18.

FIG. 2 shows, as an example, an image data set acquired with the 3-Dcamera 18 after using a voxel grid filter (see below). This is a clusterof points having a plurality of acquired pixels to each of which areassigned three coordinates so that the position in space of eachacquired individual pixel is known. FIG. 2 shows a perspectiverepresentation of the cluster of points such that the depth informationassigned to the individual pixels is only vague. However upon observingthe cluster of points in this perspective representation, it can alreadybe recognized that the acquired pixels are clustered along the dottedbolded lines 22, 24. The lines 22 characterize the progression of twohorizontal shelf supports, the line 24 characterizes the progression ofa vertical shelf support.

A first method according to the invention for evaluating the image datais described in more detail using the FIGS. 3 to 12. Initially thevolume, in which the acquired pixels are arranged, is divided into aplurality of equally sized cubes. Cubes with a uniform edge length of 20cm, for example, can be used. The acquired image points within each ofthe cubes are averaged and represent only a single image element for apart of the subsequent evaluation.

Then, angle information is calculated for each of the image elementsthat specifies an angle between a surface represented by the imageelement and a vertical reference plane. The vertical reference plane canbe the y-z plane, for example, of the coordinate system indicated inFIG. 1. In order to calculate this angle information, initially a normalvector can be calculated considering the adjacent image elements foreach image element. The angle between this normal vector and thereference plane is the required angle information.

FIG. 3 shows a histogram in which the angle information is sorted forall image elements. The 0° position on the right in the diagramcorresponds to the viewing direction of the 3-D camera 18. The angledivision revolves forming a circle about a center point of the diagram.The distance of the represented curve 26 from the center point of thediagram specifies the frequency of the individual angle information. Thehistogram is shown after a smoothing. A distinct maximum can berecognized near the −90° position.

Thus, the image data contain particularly many image elements whosenormal vectors have this angle to the reference plane. With this, themaximum of a histogram characterizes a predominant direction 66 in theacquired image data. Because the 0° direction corresponds to the viewingdirection of the 3-D camera, this means that particularly many imageelements were acquired that are aligned somewhat perpendicular to theviewing direction of the camera. In other words, the 3-D camera 18 inthe represented example views approximately directly in front ofrelatively large surface structures, approximately on a wall surface ora front shelf plane.

After determining the predominant direction 66 based on the datarepresented in FIG. 3, with the first method according to the inventiona further evaluation is performed based on the originally acquired imagedata (as represented in FIG. 2). Positions along the predominantdirection 66 are calculated for each of the acquired pixels. Thesepositions can specify, for example, the distances to the 3-D camera 18measured along the predominant direction 66. In addition, anotherreference plane that is perpendicular to the predominant direction 66can be used as an origin for this position determination.

The positions of the acquired pixels along the predominant direction 66,calculated in this manner, are illustrated in the FIGS. 4 and 5 infurther histograms. In the example of FIG. 4, two clearly distinctmaximums 30, 32 can be seen that are located at distances ofapproximately 3.5 m and approximately 5 m from the 3-D camera 18. Itshould be noted that considering a tolerance, no pixels are recorded atdistances greater than the first maximum 30 at approximately 5 m. Thisindicates that the first maximum 30 is a wall plane. The second maximum32 is located approximately 1.5 m closer to the 3-D camera 18 in thepredominant direction 66 than the first maximum 30. This indicates thatthe second maximum 32 is a front shelf plane 14 of a shelf 12 that is infront of the wall surface 10.

FIG. 5 shows another example in which only a single maximum is arrangedat a third position of approximately 3.3 m. At greater distanceshowever, in contrast to the first maximum 30 of FIG. 4, there are acertain number of further acquired pixels. This can be interpreted suchthat the single maximum 34 is also a shelf front plane 14; theassociated shelf 12 is however not placed in front of a wall surface 10or the wall surface 10 is not visible through the shelf 12.

In a next evaluation step, the pixels acquired in a surrounding area ofa main plane are projected onto this main plane, and preferably alongthe predominant direction 66. FIG. 6 shows the results of the example ofa shelf front plane 14. After the projection, the data aretwo-dimensional. Dark pixels indicate that at least one pixel wasacquired at the respective position in the surrounding area of the shelffront plane 14. The further evaluation can occur using these projected,two-dimensional data which significantly reduces the computationalexpense.

For this purpose, with the first method according to the invention, acomparison of the projected, two-dimensional data from FIG. 6 isperformed with predefined templates. The FIGS. 7 to 9 show three suchpredefined templates, namely FIG. 7 shows a template of a horizontalshelf support, FIG. 8 shows a template of a vertical shelf support, andFIG. 9 shows a template of a pallet. These predefined templates arecompared with the image data of FIG. 6, in that they are placed atdifferent positions over the image data and the number of coincidingpixels are determined In particular, the predefined templates with thecenter points thereof can be placed at the position of each individualpixel of FIG. 6 (with the exception of an edge region).

The results of such a procedure are shown in FIGS. 10 to 12. The pointsappearing dark in these figures show positions of the predefinedtemplate relative to the image data at which the similarity isparticularly high. It can be seen in FIG. 10, which shows a comparisonto the template of FIG. 7, that distinct horizontal running dark stripes36 are located just below the upper edge of the image and approximatelyin the middle of the image. These are traced back to horizontal shelfsupports. FIG. 11 shows the results of the comparison to the template ofFIG. 8. A noticeable vertical running dark stripe 38 arranged somewhatto the right of the center of the image specifies the position of avertical shelf support.

FIG. 12 shows the results of the comparison to the template of FIG. 9.Points with particularly high agreement with the template of FIG. 9representing a pallet are emphasized by small arrows. A careful observerrecognizes by comparison with FIG. 6, that at all arrows located in theupper and right region of the image are actually the center points ofthe pallets that can be recognized in FIG. 6. The arrow located belowleft however is not at the position of a pallet in FIG. 6, but rather isapparently an accidental agreement of structures acquired in this imageregion tracing back to the template of FIG. 9.

In order to avoid detecting a pallet at this position in the furtherprocedure, a plausibility control can be performed. For example, afurther criterion can be required that objects to be detected as apallet are arranged within a specific distance above a horizontal shelfsupport or the floor. This criterion would not be satisfied at theposition of the arrow represented below left in FIG. 12 such that theaccidental agreement of the structure acquired there would not lead tothe detection of a pallet.

A second method according to the invention is described in more detailusing the FIGS. 13 to 16. The starting point of the evaluation is againan image data set provided by the 3-D camera 18, wherein with thismethod each acquired pixel is assigned not only three-dimensionalcoordinates thereof, but additionally also a color value. Appropriateimage data is provided, for example, by the Microsoft Kinect camera,mentioned above. As a first evaluation step, there is a segmenting ofthe image data based on these color values. For this purpose aFelzenszwalb-Huttenlocher algorithm is used which operates on the colorsof the cluster of points. In this manner the acquired pixels aresubdivided into a plurality of segments, where there is a logicalcorrelation between the acquired pixels of each segment. In FIG. 13,instead of a color representation typical for the purposes ofpresentation, only the contours are represented between adjacentsegments.

Then, segment attributes are calculated for each segment. For thispurpose, the dimensions of the segments in three dimensions, forexample, can be used. These can be calculated based on the pixelsbelonging to the segment, as shown in FIG. 14. Here, a cube, forexample, in which lie all pixels belonging to the segment, can becalculated. In this manner, a width b, height h and a depth t areobtained for the segment.

A relative depth information is a further helpful segment attribute forthe later classification. This is explained using FIG. 15. The 3-Dcamera 18 can be seen on the left, and a wall surface 10 can be seencompletely on the right. An object 40 that is represented as a segmentis located between the two. The distance between the 3-D camera 18 andwall surface 10 is referred to as z_(max). The distance between the 3-Dcamera 18 and object 40 is referred to as z_(object). The relative depthinformation is referred to as z_(rel), and results in the differencez_(max)−z_(Object).

After the calculation of the segment attributes for each segment thereis a classification of the segments using a support vector machine. Theresult of this classification is shown in FIG. 16 in which theidentified classes are illustrated using different gray values. Thedarkest level of gray 42 corresponds to the vertical shelf supportclass. The segments classified as such form a vertical stripe 56 in theFIG. 16.

The second darkest level of gray 44 illustrates the horizontal shelfsupport class. The segments classified as such are located in twohorizontal running stripes 58 in FIG. 16 (considering the perspectiverepresentation).

The third darkest level of gray 46 corresponds to the sign class.Segments 60 detected as such are located most noticeably above the lowerhorizontal shelf support and to the right of the vertical shelf support.They are located at the front side of further segments 62, which wereclassified as transport boxes, represented by the next lighter level ofgray 48.

A further level of gray 50 represented in FIG. 16 corresponds to thewall surface class. Corresponding segments 64 can be seen, inparticular, within the shelf compartments formed between the individualshelf supports.

A still lighter level of gray 52 is for the pallet class, and in FIG. 16is located predominantly below the segments 62 classified as a transportboxes. The legend comprises yet a further level of gray 54 which standsfor a class not further described here.

1. A method for detecting objects in a warehouse and/or for spatialorientation in a warehouse having the following steps: acquiring imagedata with a 3-D camera which is fastened to an industrial truck so thata viewing direction of the 3-D camera has a defined angle to thehorizontal, wherein the 3-D camera has an image sensor with sensorelements arranged matrix-like and the image data comprises a pluralityof pixels, wherein distance information is assigned to each pixel,calculating angle information for a plurality of image elements, whicheach specify an angle between a surface represented by the image elementand a vertical reference plane, determining a predominant directionbased on the frequencies of the calculated angle information,calculating the positions of the acquired pixels along the predominantdirection, detecting at least one main plane of the warehouse based on afrequency distribution of the calculated positions.
 2. The methodaccording to claim 1, wherein the image elements for which the angleinformation is calculated, are calculated in each case using averagingover all pixels contained in a predefined volume element.
 3. The methodaccording to claim 1, wherein one of the main planes is a wall plane,which is detected at a first position and perpendicular to thepredominant direction, if the frequency distribution at the firstposition has a first maximum and the number of pixels with positionsfurther remote from the 3-D camera is less than a predefined first limitvalue.
 4. The method according to claim 3, wherein one of the mainplanes is a shelf front plane, which is detected at a second positionand perpendicular to the predominant direction, if the frequencydistribution at the second position has a second maximum and the secondposition is arranged closer to the 3-D camera by 0.9 m to 1.7 m than thefirst position.
 5. The method according to claim 1, further comprisingone of the main planes is a shelf front plane, which is detected at athird position and perpendicular to the predominant direction, if thefrequency distribution has only a single distinct maximum that isarranged at the third position, and the number of pixels with positionsfurther remote from the 3-D camera is greater than a predefined secondlimit value.
 6. The method according to claim 1, further comprising thefurther steps: projecting the pixels, which lie in a surrounding area ofa detected main plane onto this main plane and detecting objects of thewarehouse using comparison of the projected, two-dimensional data withpredefined templates.
 7. A method for detecting objects in a warehouseand/or for spatial orientation in a warehouse having the followingsteps: acquiring image data with a 3-D camera which is fastened to anindustrial truck so that a viewing direction of the 3-D camera has adefined angle to the horizontal, wherein the 3-D camera has an imagesensor with sensor elements arranged matrix-like and the image datacomprises a plurality of pixels, wherein a color value and distanceinformation is assigned to each pixel, segmenting the image data intocontiguous segments based on the color values, calculating segmentattributes for each segment, classifying the segments based on thesegment attributes, detecting a warehouse object based on theclassification.
 8. The method according to claim 7, wherein one or moreof the following properties are used as segment attributes: dimensions(b, h, t) average color value, number of pixels, relative depthinformation (Z_(rel)).
 9. The method according to claim 7, furthercomprising a support vector machine is used for the classification. 10.The method according to claim 7, wherein with the classification ofsegments, one or more of the following classes are considered: verticalshelf supports, horizontal shelf supports, signs, transport boxes,walls, pallets.
 11. The method according to claim 10, wherein segmentslying above one another, which were classified as vertical shelfsupports, and/or segments lying next to each other, which wereclassified as horizontal shelf supports, are respectively combined intoa segment group.
 12. The method according to claim 10, furthercomprising a segment is detected as a pallet if the following criteriaare satisfied: the segment was classified with a minimum probability asa pallet and/or a center point of the segment is located within apredefined height range above a horizontal shelf-support and within apredefined distance range behind the front thereof and/or a comparisonof the front side of the segment with a predefined template of a palletyields a minimum degree of similarity.
 13. The method according to claim1, further comprising a vacant warehouse space is detected if no pixels,or respectively segments, are present in a defined spatial region abovean object that was detected or classified as a horizontal shelf support.14. The method according to claim 1, further comprising the dimensions(b, h, t) of a load are determined by evaluating the pixels, orrespectively segments, acquired above an object detected as a pallet.15. The method according to claim 1, further comprising the industrialtruck has a navigation system that provides position data for theposition of the industrial truck in the warehouse, and that the positiondata are modified considering a detected main plane and/or a detectedobject.
 16. The method according to claim 1, further comprising the 3-Dcamera is a time-of-flight camera or a camera system that projects andmaps a defined template on the image field and that determines thedistance information from a shift of the template.
 17. An industrialtruck with an apparatus for detecting objects in a warehouse and/or forspatial orientation in a warehouse, wherein the apparatus comprises thefollowing: a 3-D camera for acquiring image data, wherein the 3-D camerais fastened to the industrial truck so that a viewing direction of the3-D camera has a defined angle to the horizontal, an image sensor havingsensor elements arranged matrix-like and the image data comprises aplurality of pixels, to each of which distance information is assigned,an evaluation apparatus for evaluating the image data that is designedfor the purpose of calculating angle information, which each specify anangle between a surface represented by the image element and a verticalreference plane, for a plurality of image elements, determining apredominant direction based on the frequencies of the calculated angleinformation, calculating positions of the acquired pixels along thepredominant direction, and detecting at least one main plane of thewarehouse based on a frequency distribution of the calculated positions.18. An industrial truck having an apparatus for detecting objects in awarehouse and/or for spatial orientation in a warehouse, wherein theapparatus comprises the following: a 3-D camera for acquiring imagedata, wherein the 3-D camera is fastened to the industrial truck so thata viewing direction of the 3-D camera (18) has a defined angle to thehorizontal, has an image sensor with sensor elements arrangedmatrix-like and the image data comprises a plurality of pixels, to eachof which a color value and distance information is assigned, anevaluation apparatus for evaluating the image data that is designed forthe purpose of segmenting the image data into contiguous segments basedon the color values, calculating segment attributes for each of thesegments, classifying the segments based on the segment attribute, anddetecting a warehouse object based on the classification.